White light‐emitting diode (LED) luminous efficacy must improve significantly if LEDs are to become useful for general lighting. Phosphors commonly used in white LEDs backscatter more than half of the down‐converted light, of which a significant portion is eventually lost within the package, thus reducing the overall efficacy. This letter describes an experi‐mental study that shows by placing the phosphor away from the die, the backscattered photons can be extracted and the ef‐ficacy can be significantly increased. At low currents, the lu‐minous efficacy exceeded 80 lm/W. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A uni® ed system of photometry is proposed that is based on human vision and allows the speci® cation of visual stimuli at all light levels. To be useful, however, photometry can never be entirely synonymous with vision. Additivity is an essential characteristic of photometry, yet many visual responses, such as brightness matching, incorporate visual channels that are inherently non-additive in responding to light. Following a review of models of mesopic photometry based on a number of experimental techniques, a system of photometry based on reaction times is proposed to bridge conventional photopic and scotopic luminous ef® ciency functions through the mesopic region. The basis for the uni® ed system is a parameter, X, which describes the proportion of photopic luminous ef® cacy at any luminance, and luminance can be calculated from a simple closed-form equation. The utility of the system is described, including instrumentation for the measurement of uni® ed luminance.

This ® eld study uses a new model home demonstrating good lighting-design principles with energy-ef® cient solutions. Surveys showed that builders and the general public accepted and even preferred the appearance and the lighting effects of energy-ef® cient lighting technologies. Key to the success was integration with architectural features, colour schemes, and user lifestyle. Detailed survey results, energy savings, and illuminance comparisons are presented, as well as a discussion of ongoing barriers to the use of energy-ef® cient technology. Designers sharè lessons learned' from this design case study.

No abstract

No abstract